If sugary drinks were sold in smaller bottles, stores stocked fewer of them, and positioned them less prominently, we would drink fewer of them. But would we find these changes acceptable? The results of our recent study show that most people find these “nudges” (altering cues in the environment to change people’s behaviour) to be acceptable ways to prevent obesity. Taxing sugary drinks, however, was only acceptable to a minority.

But for both nudging and taxing, the acceptability of the intervention increased the more effective participants judged them to be. This suggests that people are prepared to trade off their dislike of an intervention for achieving a goal they value, such as tackling obesity.

Sugary drinks are consumed more by the poorest in society explaining, in part, the higher rates of obesity in this group. Unfortunately, educating people about the health harms of consuming an excess of sugary drinks – an intervention that most people find acceptable – does not reduce their consumption.

But the evidence is now growing that “nudges” as well as taxes could reduce consumption of sugary drinks. The recent announcement of a tax on sugary drinks in England comes with much public support, and the case is made more compelling by recent evidence from Mexico that taxing drinks reduces consumption, particularly among the poor. But obesity won’t be cracked by tax alone. Adding nudges to taxes would likely help, but the acceptability of nudging has, until now, been largely unknown.

In New York, a recent attempt to cap the size of sugary drinks sold in restaurants and other food outlets elicited a strong reaction from locals. But these views may have been influenced by campaigns run by industry-funded consumer groups that placed adverts on billboards and in newspapers asserting that this measure undermined individual freedom. Given that introducing these sorts of interventions will probably require regulation, it is important to gauge public acceptability outside of the context of a media campaign in one city.

Change the environment, change the behaviour

For our study, we recruited 1,093 participants from the UK and 1,082 from the US.

We compared the acceptability of three nudge interventions (reducing the size of sugary drinks bottles, elongating the shape of cans of sugary drinks so they look larger than current cans, and altering where on the shelf drinks were placed) with two more traditional interventions: education and taxation.

Education was the most accepted intervention (more than 80% of participants considered it to be acceptable), taxation the least (fewer than 46% judged it acceptable), and the nudge interventions rated between these (range: 51% to 68%).

Highlighting the unconscious nature of nudges did not reduce their acceptability. Nudging is more acceptable than taxation, but the acceptability of both may be sensitive to evidence of their effectiveness.

Perceived effectiveness was the strongest predictor of acceptability for all interventions across both the US and UK groups. In other words, the more effective people perceived an intervention to be, the more acceptable they found it. This replicates findings from other studies.

Mexico provides an interesting case study. With funding from Bloomberg Philanthropies, non-governmental organisations bought prominent advertising space to counter industry opposition to sugary drinks taxes. This included presenting evidence of taxation’s effectiveness at preventing obesity and other consequences of high consumption. This supports the idea that clear communication to the public of an intervention’s effectiveness – in this case, taxing sugary drinks – can increase public acceptability of the intervention. This may then lead politicians to implement the intervention.

Attributing obesity to the environment, rather than willpower, also predicted acceptability. The more people attributed over-consumption to the environment, the greater their support for interventions, particularly the three nudge interventions. This suggests that the public’s judgements of nudging could become even more favourable if we can successfully convey scientific understandings of human behaviour. This would result in people understanding that much of our behaviour, that is shaped by the environment, takes place outside of conscious awareness. Changing the environment could therefore help tackle obesity.